Motor drive system and control method for chiller unit

Abstract

The present application relates to air conditioning technology and motor control technology, and in particular to a motor drive system for a chiller unit, a chiller unit comprising the motor drive system, a control method for a chiller unit, and a computer-readable storage medium on which is stored a computer program for implementing the method. A motor drive system for a chiller unit according to an aspect of the present application comprising: a variable frequency drive unit configured to drive a first motor; a power frequency drive unit configured to drive a second motor; and a control unit configured to adapt a load demand of the chiller unit by controlling output power of the variable frequency drive unit and the power frequency drive unit.

What is claimed is: 
     
         1 . A motor drive system for a chiller unit, the chiller unit comprising a first compressor, a first motor for the first compressor, a second compressor and a second motor for the second compressor, the motor drive system comprising:
 a variable frequency drive unit configured to drive the first motor;   a power frequency drive unit configured to drive the second motor; and   a control unit configured to adapt a load demand of the chiller unit by controlling output power of the variable frequency drive unit and the power frequency drive unit.   
     
     
         2 . The motor drive system of  claim 1 , wherein a rated power of the first compressor is greater than or equal to a rated power of the second compressor. 
     
     
         3 . The motor drive system of  claim 1 , wherein the number of the first compressors is one and the number of the second compressors is one or more. 
     
     
         4 . The motor drive system of  claim 1 , wherein the control unit controls the output power of the variable frequency drive unit and the power frequency drive unit in the following manner:
 adapting the load demand by operating only the variable frequency drive unit when the load demand is less than or equal to a first critical value, wherein the variable frequency drive unit is operated at a variable output power;   adapting the load demand by operating the variable frequency drive unit and the power frequency drive unit when the load demand is greater than a second critical value and less than a third critical value, wherein the variable frequency drive unit is operated at a first output power and the power frequency drive unit is operated at a variable output power, wherein the second critical value is greater than or equal to the first critical value; and   adapting the load demand by operating the variable frequency drive unit and the power frequency drive unit when the load demand is greater than or equal to the third critical value, wherein the variable frequency drive unit is operated at a variable output power and the power frequency drive unit is operated at a second output power.   
     
     
         5 . The motor drive system of  claim 4 , wherein the first output power is less than the output power of the variable frequency drive unit when the load demand is equal to the first critical value, and the second output power is equal to a maximum output power of the power frequency drive unit. 
     
     
         6 . The motor drive system of  claim 4 , wherein the first compressor and the second compressor are same types of compressors, the chiller unit is a screw chiller unit, and the first critical value is 50% of a rated load demand of the screw chiller unit. 
     
     
         7 . The motor drive system of  claim 4 , wherein the first compressor and the second compressor are different types of compressors, the chiller unit is a screw chiller unit, and the first critical value is 40% of a rated load demand of the screw chiller unit. 
     
     
         8 . A chiller unit comprising:
 a first compressor;   a first motor for the first compressor;   a second compressor;   a second motor for the second compressor; and   a motor drive system as claimed in  claim 1 .   
     
     
         9 . A control method for a chiller unit, the chiller unit comprising a first compressor, a first motor for the first compressor, a second compressor and a second motor for the second compressor, the method comprising:
 utilizing a variable frequency drive unit and a power frequency drive unit to drive the first motor and the second motor respectively, wherein a load demand of the chiller unit is adapted by controlling output power of the variable frequency drive unit and the power frequency drive unit.   
     
     
         10 . The method of  claim 9 , wherein a rated power of the first compressor is greater than or equal to a rated power of the second compressor. 
     
     
         11 . The method of  claim 9 , wherein the number of the first compressors is one and the number of the second compressors is one or more. 
     
     
         12 . The method of  claim 9 , wherein the output power of the variable frequency drive unit and the power frequency drive unit is controlled in the following manner:
 adapting the load demand by operating only the variable frequency drive unit when the load demand is less than or equal to a first critical value, wherein the variable frequency drive unit is operated at a variable output power;   adapting the load demand by operating the variable frequency drive unit and the power frequency drive unit when the load demand is greater than a second critical value and less than a third critical value, wherein the variable frequency drive unit is operated at a first output power and the power frequency drive unit is operated at a variable output power, wherein the second critical value is greater than or equal to the first critical value; and   adapting the load demand by operating the variable frequency drive unit and the power frequency drive unit when the load demand is greater than or equal to the third critical value, wherein the variable frequency drive unit is operated at a variable output power and the power frequency drive unit is operated at a second output power.   
     
     
         13 . The method of  claim 12 , wherein the first output power is less than the output power of the variable frequency drive unit when the load demand is equal to the first critical value, and the second output power is equal to a maximum output power of the power frequency drive unit. 
     
     
         14 . The method of  claim 12 , wherein the first compressor and the second compressor are same types of compressors, the chiller unit is a screw chiller unit, and the first critical value is 50% of a rated load demand of the screw chiller unit. 
     
     
         15 . The method of  claim 12 , wherein the first compressor and the second compressor are different types of compressors, the chiller unit is a screw chiller unit, and the first critical value is 40% of a rated load demand of the screw chiller unit. 
     
     
         16 . A computer-readable storage medium, the computer-readable storage medium having instructions stored therein, characterized in that the instructions, when executed by a processor, cause the processor to perform a method as claimed in  claim 9 .